Systematical Search for remotely triggered earthquakes in Tibet Plateau following the 2004 M9.2 Sumatra and the 2005 M8.6 Nias earthquake

The continuous collision between the Indian Plate and Eurasian Plate gives rise to the formation of Tibet Plateau, one of the most complex tectonic environments in the world. In this study, we search for remotely triggered earthquakes in Tibet Plateau following the 2004 M9.2 Sumatra and the 2005 M8.6 Nias Earthquakes. During 2002 to 2005, the Hi-CLIMB (Himalayan-Tibetan Continental Lithosphere during Mountain Building) experiment (IRIS network code XF) was operated in South-Central Tibet, extending from the Ganges lowland, across the Himalayas and into the central Tibetan plateau. Over 200 sites were occupied over this experiment, providing unprecedented continuous recordings around the 2004 Sumatra and the 2005 Nias Earthquakes. On April 7th 2005, nearly 10 days after the 2005 Nias Earthquake, Zhongba was shaken by an Mw 6.3 Earthquake, raising the question on whether this event was delay-triggered by the Nias Earthquake. The Zhongba region is characterized by many NS-trending rift systems that accommodate EW extension, and several moderate-size earthquakes since 2004 suggest that this region is seismically active. Here we use a recently developed matched filter technique to examine seismicity rate changes associated with the 2004 Sumatra and 2005 Nias earthquakes. Specifically, we use 32 relocated earthquakes in Zhongba as templates to detect additional local events between 12/2004 and 05/2005. Although we have detected more than 45 times more events during this time period, we find no statistically significant change in the seismicity rate following the Nias earthquake and before the 2005 Zhongba mainshock. Hence, it is difficult to establish a triggering relationship between these two events. However, after manual inspection of the continuous data during the surface wave trains of the 2004 Sumatra and the 2005 Nias earthquakes, we identify many triggered microearthquakes 350 km north of Zhongba. These dynamically triggered events were located in southern part of Qiangtang Terrane. However, no moderate to large earthquakes occurred following those dynamically triggered microearthquakes. Our next step is to use the Antelope software to manually pick and locate more local events first, then use the waveform matching technique to detect additional small events, and use them to better understand the triggering behavior in Tibet Plateau.